May 11, 2011
Neanderthals May Have Died Out Earlier Than Believed
Researchers have new evidence that suggest Neanderthals died out much earlier than previously thought, and possibly before modern humans arrived.
Carbon-dated Neanderthal remains from a cave in the foothills of the Caucasus Mountains in Russia were found to be 10,000 years older than previous research had suggested. The new evidence contradicts the popular theory that Neanderthals and modern humans interacted for thousands of years before the archaic species became extinct.
Instead, the researchers believe any co-existence between the two species is likely to have been far more restricted, perhaps at most a few hundred years. It is quite possible in some areas Neanderthals became extinct before modern humans moved out of Africa.
The remains from the cave, known as Mezmaiskaya, were dated with a precise carbon-dating technique, said paleoanthropologist Thomas Higham of the University of Oxford, UK, a co-author of a study published in the Proceedings of the National Academy of Sciences.
Higham's team says the implication is that Neanderthals and humans may never have met in Europe. However, the Neanderthal genome, decoded by scientists last year, suggests that the ancestors of all humans, except those from Africa, interbred with Neanderthals somewhere.
"DNA results show that there was admixture probably at some stage in our human ancestry, but it more than likely happened quite a long time before humans arrived in Europe," says Ron Pinhasi, an archaeologist at University College Cork in Ireland, who is lead author of the latest study. "I don't believe there were regions where Neanderthals were living next to modern humans. I just don't find it very feasible."
The researchers found the fossil in question to be 39,700 years old, instead of the previous assigned 30,000 years old. The dating implies that Neanderthals did not survive at the cave site beyond that time.
The research suggests that if we are going to have accurate chronologies the data needs to be improved so possible associations between Neanderthals and early modern humans can be properly assessed. The previous dating processes seem to have "systemically underestimated" the true age of Late Middle Paleolithic and Early Upper Paleolithic deposits, artifacts and fossils by up to several thousand years, says the research report.
"The latest dating techniques mean we can purify the collagen extracted from tiny fragments of fossil very effectively without contaminating it," said Higham. "Previously, research teams have provided younger dates which we now know are not robust, possibly because the fossil has become contaminated with more modern particles."
"This latest dating evidence sheds further light on the extinction dates for Neanderthals in this key region, which is seen by many as a crossroads for the movement of modern humans into the wider Russian plains. The extinction of Neanderthals here is, therefore, an indicator we think, of when that first probably happened," said Higham.
Carbon dating of stone tools characteristic to both humans and Neanderthals, as well as their remains, has previously suggested that the first humans to reach Europe, between 40,000 and 30,000 years ago, shared the land with Neanderthals that were believed to have been long established there.
However, carbon dating of remains older than 30,000 years is tricky because nearly all the radioactive carbon in the remains has decayed, said Higham.
The overlap in dating could also be the result of contamination of older finds with younger finds. "What we are finding is that the careful and patient excavation work of many archaeological sites has not been supported by accurate and reliable radiocarbon dating," Higham said.
But, using the most up-to-date carbon-dating techniques, Pinhasi and his team were able to date the remains of two Neanderthal infants from the cave to close to 40,000 years old. The infants' bones were found above the cave's other Neanderthal remains, so they must have been the most recent, Higham explained.
Higham's conclusion fits with another discovery made by David Reich, a geneticist at Harvard Medical School in Boston, Massachusetts, whose team found that all contemporary humans, except those who trace their roots back to Africa, owe about 1 to 4 percent of their DNA to interbreeding between early modern humans and Neanderthals.
Reich's team did not find any proof that Neanderthals ever mated with the ancestors of modern Europeans specifically, however.
Yet he said that new, more sensitive methods for detecting interbreeding, as well as genome sequences from late Neanderthals could change that conclusion. "Absence of evidence isn't evidence of absence," said Reich.
Chris Stringer, a paleoanthropologist at the Natural History Museum in London, agrees that Neanderthals were rare in Europe after 40,000 years ago, but added that they might not have completely disappeared.
"It does seem that if Neanderthal populations existed after that time, they must have been small and scattered remnants," he said.
There is evidence of more recent Neanderthal settlements. Clive Finlayson, director of the Gibraltar Museum, and his colleagues have dated a Neanderthal settlement in Gorham's Cave in Gibraltar to as recently as 24,000 years ago.
"Eurasia is a big place and there doesn't seem to be any reason why populations of Neanderthals may not have survived somewhere," said Higham.
The University of Oxford and University College Cork researchers collaborated with the Laboratory of Prehistory at St Petersburg, Russia. The study was funded by Science Foundation Ireland.
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